Just once, I want to username and password prompt to say,
"Close enough."
π
Haha.. but technically they can't. Passwords are usually stored hashed (calculated through a formula,) thus nobody except the user knows what it was originally.
The server would just compare the stored hashed password with the result (which the user don't know) from the user input that also run through the same formula.
Even a single letter would make the two results wildly different.